This is an 1885 engineering draftsman tool to design new technology and solve mathematical problems.  It was made by the Polygraph Company, patented in December 8, 1885 and also patented in Europe in 1886.  Most likely it was also a college teaching instrument in the late 1800s.  Tool is made of brass and in beautiful condition.  Size is 5 inches in diameter.   It will be a highlight to any collection of antique engineering instruments.